Reaching bottom after a 2-hour-and-36-minute descent, the National Geographic explorer and filmmaker typed out welcome words for the cheering support crew waiting at the surface: "All systems OK."

Folded into a sub cockpit as cramped as any Apollo capsule, the National Geographic explorer and filmmaker is now investigating a seascape more alien to humans than the moon. Cameron is only the third person to reach this Pacific Ocean valley southwest of Guam (map)—and the only one to do so solo.

After as long as six hours in the trench, Cameron—best known for creating fictional worlds on film(Avatar, Titanic, The Abyss)—is to jettison steel weights attached to the sub and shoot back to the surface. (See pictures of Cameron's sub.)

"We're now a band of brothers and sisters that have been through this for a while," marine biologist Doug Bartlett told National Geographic News from the ship before the dive.

"People have worked for months or years in a very intensive way to get to this point," said Bartlett, chief scientist for the DEEPSEA CHALLENGE program, a partnership with the National Geographic Society and Rolex. (The Society owns National Geographic News.)

"I think people are ready," added Bartlett, of the Scripps Institution of Oceanography in San Diego, California. "They want to get there, and they want to see this happen."

Upon touchdown at Challenger Deep, Cameron's first target is a phone booth-like unmanned "lander" dropped into the trench hours before his dive.

Using sonar, "I'm going to attempt to rendezvous with that vehicle so I can observe animals that are attracted to the chemical signature of its bait," Cameron told National Geographic News before the dive.

He'll later follow a route designed to take him through as many environments as possible, surveying not only the sediment-covered seafloor but also cliffs of interest to expedition geologists.

Though battery power and vast distances limit his contact with his science team to text messaging and sporadic voice communication, Cameron seemed confident in his mission Friday. "I'm pretty well briefed on what I'll see," he said.

To get to this point, Cameron and his crew have spent seven years reimagining what a submersible can be. The result is the 24-foot-tall (7-meter-tall) DEEPSEA CHALLENGER.

Engineered to sink upright and spinning, like a bullet fired straight into the Mariana Trench, the sub can descend about 500 feet (150 meters) a minute—"amazingly fast," in the words of Robert Stern, a marine geologist at the University of Texas at Dallas.

By contrast, some current remotely operated vehicles, or ROVs, descend at about 40 meters (130 feet) a minute, added Stern, who isn't part of the expedition.

Andy Bowen, project manager and principal developer of the Nereus, an ROV that explored Challenger Deep in 2009, called the DEEPSEA CHALLENGER "an extremely elegant solution to the challenge of diving a human-occupied submersible to such extreme depths."

"It's been engineered to be very effective at getting from the surface to the seafloor in as quick a time as possible," said Bowen, of Woods Hole Oceanographic Institution, who also isn't part of the current expedition.

Pursuing speed and science in tandem makes the DEEPSEA CHALLENGER test dives—and even the Mariana Trench mission—perhaps as unorthodox as the sub itself.

Typically "you conduct a sea trial for a vehicle, you pronounce it fit for service, and then you develop a science program around it," Cameron said before heading to the trench. "We collapsed that together into one expedition, because [we were] fairly confident the vehicle would work—and it is."

Techno Torpedo

Now, at the bottom of the trench, the sub's custom-designed foam filling and the pressure-resistant shape of the "pilot sphere"—are helping protect Cameron from the equivalent of 8 tons pressing down on every square inch (1,125 kilograms per square centimeter). (Video: how sub sphere protects Cameron.)

Among the sub's tools are a sediment sampler, a mechanical claw, a "slurp gun" for sucking up small sea creatures for study at the surface, and temperature, salinity, and pressure gauges.

While that might sound like a gearhead's paradise, Cameron knows he'll "have to be able to prioritize."

"Is my manipulator working properly? Do I still have room in my sample drawer? And do I still have the ability to take a [sediment] core sample? ... I only have [tools for] three sediment cores available on the vehicle, so I have to choose wisely when to use them."

By contrast, the sub's multiple 3-D cameras will be whirring almost continually, and not just for the benefit of future audiences of planned documentaries.

"There is scientific value in getting stereo images," Cameron said, "because ... you can determine the scale and distance of objects from stereo pairs that you can't from 2-D images."

But, Scripps's Bartlett said, "it's not just the video." The sub's lighting of deepwater scenes—mainly by an 8-foot (2.5-meter) tower of LEDs—is "so, so beautiful. It's unlike anything that you'll have seen from other subs or other remotely operated vehicles."

"If we get lucky," Cameron said before the dive, "we should find something like a cold seep, where we might find tube worms." Cold seeps are regions of the ocean floor somewhat like hydrothermal vents (video) that ooze fluid chemicals at the same temperature as the surrounding water.

Earlier this month, during a test dive near Papua New Guinea, Cameron brought back enormous shrimplike creatures from five miles (eight kilometers) down. At 7 inches (17 centimeters) long, the animals are "the largest amphipods ever seen at that kind of depth," chief scientist Bartlett said. "And we saw one on camera that was perhaps twice that size."

At Challenger Deep depths, though, the calcium animals need to form shells dissolves quickly. It's unlikely—though not impossible—that Cameron is finding shelled creatures, but if he does, the discovery would be a scientific jaw-dropper.

Even if he uncovers "a rock with a shell limpet or some kind of bivalve in the mud"—such as a clam, perhaps—"that would be exciting," Scripps's Levin said.

Aliens of the Abyss

Expedition astrobiologist Kevin Hand, of NASA, imagines that the life-forms Cameron might be encountering could help fine-tune the search for extraterrestrial life.

For instance, scientists think Jupiter's moon Europa could harbor a global ocean beneath its thick shell of ice—an ocean that, like Challenger Deep, would be lightless, near freezing, and home to areas of intense pressure. (See "Could Jupiter Moon Harbor Fish-Size Life?")

By studying the wavelengths of light, or spectra, reflected off life-forms and sediments brought up by Cameron, Hand should get a better idea of which minerals are needed for life in such an environment. This, in turn, might help him design a space probe better able to detect signs of life on Europa.

"I think astrobiology could have a similar adage, in that our best capability for finding life elsewhere—and knowing it when we see it—will come from having a comprehensive understanding of all the various extremes of life on Earth."

While ROVs are much less expensive than manned subs, "the critical thing is to be able to take the human mind down into that environment," expedition member Patricia Fryer said, "to be able to turn your head and look around to see what the relationships are between organisms in a community and to see how they're behaving—to turn off all the lights and just sit there and watch and not frighten the animals, so that they behave normally.

"That is almost impossible to do with an ROV," said Fryer, a marine geologist at the Hawai'i Institute of Geophysics & Planetology.

In fact, Cameron is so confident in his star vehicle that he started mulling sequels even before the trench dive.

Phase two might include adding a thin fiber-optic tether to the ship, which "would allow science observers at the surface to see the images in real time," he said. "And phase three might be taking this vehicle and creating a second-generation vehicle."

DEEPSEA CHALLENGE, then, may be anything but a one-hit wonder. ToBartlett, the Mariana Trench expedition could "represent a turning point in how we approach ocean science.

"I absolutely think that what you're seeing is the start of a program, not just one grand expedition."

Rachael Jackson of National Geographic Channels International contributed reporting to this story.

Additional major support for the DEEPSEA CHALLENGE expedition was provided by the Alfred P. Sloan Foundation.